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AI Summary. Global fertility has fallen below replacement level, meaning population will peak at roughly 9 billion around 2056 and then decline, driven by large existing generations masking the underlying shortfall in births.
Jesús Fernández-Villaverde and Patrick Norrick University of PennsylvaniaCore argument: Global fertility has fallen below replacement level as of 2026, ending humanity’s ability to sustain long-run population stability without a reversal in trends.
In Table A1 we compare the World Population Prospects (WPP) estimates of births in 2022-2023 with the official numbers reported by several countries. [A2 shows the full sample with the deviations.] As of 2026, humanity is likely to be below the replacement fertility level: we are having fewer births than we need to keep population constant in the long run. This astonishing fact does not mean that population has stopped growing. Because of momentum effects (the large cohorts of women born two or three decades ago are having their children now, and their own parents have not died yet), world population will keep growing for another 30 years or so. But unless trends change, it will peak at roughly 9 billion around 2056 and then start falling, first slowly, then fast.AI Summary. Intermarriage across racial and ethnic lines is rising across all major demographic groups in the United States, producing a growing share of the population that does not fit neatly into any single government-defined racial or ethnic category.
Justin Fox BloombergCore argument: Post-1960s immigration from Asia and Latin America is the primary driver of rising U.S. demographic diversity and the declining non-Hispanic White population share.
The increase in immigration from Asia and Latin America since the 1960s has been the chief driver of the rise in diversity and decline in the non-Hispanic White share of the population. But those immigrants have been doing what generations of immigrants before them did and, well, becoming Americans. Marriages across racial and ethnic lines are much more prevalent among Hispanic and Asian Americans than Black or non-Hispanic White Americans, while intermarriage rates have been rising steadily for the latter two groups, too. As a result, a growing share of Americans just isn’t going to fit neatly into any single racial or ethnic category that the US government can come up with.AI Summary. A surge in labor force entrants during the 1970s created a persistent worker glut that suppressed wages and hiring demand for decades, as the oversupply remained embedded in the workforce until retirement rather than dissipating at entry.
Steven Ruggles Proceedings of the National Academy of SciencesCore argument: Baby-boom labor-force entry during 1960–1980 suppressed young-worker wages, which declined sharply after peaking in 1973, reducing economic opportunity for new.
Figure 3A highlights the influx of workers that occurred between 1960 and 1980, as the large baby-boom cohort entered the labor force, female labor-force participation expanded, and immigration rose [see Figure 2 for a detailed breakdown]. It was difficult for the economy to absorb all the new workers, and wages for young people declined sharply after peaking in 1973. Figure 3A does not, however, provide a valid measure of labor-market competition because the baby boomers and newly employed women and immigrants did not suddenly vanish after they entered the labor force; they kept working and occupying jobs until they eventually retired decades later. The glut of workers entering the labor force in the 1970s would continue to stifle demand for new workers until their eventual exit from the labor force, a process that is still in progress. The index of employment competition shown in Figure 3B is [a better] measure of relative cohort size than 3A. It represents the cumulative net labor-market entries over the previous five decades as a % of the working-age population in the current decade. As shown in Figure 1C, we are already seeing signs of an uptick in the wages of young workers, and as the demographic shortage accelerates we may finally see real wages of the young exceed the levels of the early 1970s.AI Summary. Population forecasts are dominated by model choice, not parameter uncertainty, with model selection accounting for up to 98% of output variance across projections. Different modeling approaches produce wildly divergent outcomes—from under 4bn to over 15bn people by 2075—making demographic projections tools for exploring possibilities rather than reliable predictions.
Samuele Lo Piano, Marta Kuc-Czarnecka, Roger Pielke, and Andrea Saltelli Social Science Research NetworkCore argument: Model choice accounts for 98% of output variance in 2050 global population projections, driving divergent forecasts ranging from 4–25 billion.
We explore demographic predictions by propagating all plausible choices that can be made during the analysis through the modelling process. This approach involves navigating the so-called ’garden of forking paths’—mimicking in silico what would happen if multiple investigators were to examine the same problem. For this, we now abandon [the Chinese government mathematician] Song Jian’s ‘historic’ model and turn to models currently in use: the Cohort-Component and UN WPP models, the Lee-Carter model and the Lotka-Volterra model. Note that in standard use, these tools are used in isolation, see e.g. the FAO’s How to Feed the World in 2050, resting on a single UN WPP population trajectory shielding the reader from the compounding effect of their uncertainty. Unsurprisingly, the exercise capturing the modelling of the modelling process for global population projections to 2050 and 2075 reveals distinct characteristics regarding the sensitivity and projection outcomes of the different models. Once abandoned the straitjacket of Song’s approach, uncertainty is free to manifest itself. The overall uncertainty distributions of the projected populations show a wide range of possible outcomes, reflecting the inherent uncertainties in demographic projections.AI Summary. The Midwest's brain drain is intensifying, with the income gap between those leaving and those arriving tripling from $5.6K to $15.6K (in real terms), while college-educated adults now make up 57% of out-migrants, up from 40% two decades ago.
Aziz Sunderji Home EconomicsCore argument: Illinois high-earner out-migration surged +54K annually (2014–15 to 2023–24) while low-earner departures fell -104K, driving regional brain drain toward higher-income.
Take Illinois, the most populous Midwestern state: my analysis of Census Bureau microdata shows that between 2014–15 and 2023–24, annual out-migration by households earning under $50K fell by 104K. Out-migration by Illinois households earning over $200K rose by 54K over the same period. Across the region, the trend along educational lines is the same: the bachelor’s-or-higher share of adult out-migrants is now 57%, up from around 40% in 2005. It’s the most educated and highest-earning that are still leaving in droves.